首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3364篇
  免费   458篇
  国内免费   3篇
耳鼻咽喉   33篇
儿科学   55篇
妇产科学   169篇
基础医学   246篇
口腔科学   217篇
临床医学   565篇
内科学   791篇
皮肤病学   22篇
神经病学   237篇
特种医学   72篇
外科学   224篇
综合类   44篇
预防医学   675篇
眼科学   53篇
药学   112篇
肿瘤学   310篇
  2024年   24篇
  2023年   87篇
  2022年   41篇
  2021年   85篇
  2020年   117篇
  2019年   63篇
  2018年   140篇
  2017年   130篇
  2016年   151篇
  2015年   165篇
  2014年   187篇
  2013年   241篇
  2012年   135篇
  2011年   157篇
  2010年   146篇
  2009年   204篇
  2008年   131篇
  2007年   123篇
  2006年   137篇
  2005年   121篇
  2004年   102篇
  2003年   89篇
  2002年   93篇
  2001年   52篇
  2000年   60篇
  1999年   69篇
  1998年   58篇
  1997年   58篇
  1996年   54篇
  1995年   38篇
  1994年   29篇
  1993年   30篇
  1992年   47篇
  1991年   35篇
  1990年   42篇
  1989年   41篇
  1988年   40篇
  1987年   22篇
  1986年   23篇
  1985年   24篇
  1984年   32篇
  1983年   24篇
  1982年   11篇
  1981年   9篇
  1979年   15篇
  1978年   12篇
  1974年   16篇
  1973年   9篇
  1972年   12篇
  1971年   17篇
排序方式: 共有3825条查询结果,搜索用时 15 毫秒
31.
Our aim was to test the normality of physical activity patterns and energy expenditures in normal weight and overweight primary school students. Heart rate estimates of total daily energy expenditure (TEE), active energy expenditure (AEE), and activity patterns were made over 3 consecutive school days in healthy middle-class Tunisian children (46 boys, 44 girls, median age (25th-75th) percentile, 9.2 (8.8-9.9) years. Our cross-section included 52 students with a normal body mass index (BMI) and 38 who exceeded age-specific BMI limits. TEE, AEE and overall physical activity level (PAL) were not different between overweight children and those with a normal BMI [median values (25th-75th) 9.20 (8.20-9.84) vs. 8.88 (7.42-9.76) MJ/d; 3.56 (2.59-4.22) vs. 3.85 (2.77-4.78) MJ/d and 1.74 (1.54-2.04) vs. 1.89 (1.66-2.15) respectively]. Physical activity intensities (PAI) were expressed as percentages of the individual’s heart rate reserve (%HRR). The median PAI for the entire day (PAI24) and for the waking part of day (PAIw) were lower in overweight than in normal weight individuals [16.3 (14.2-18.9) vs. 20.6 (17.9-22.3) %HRR, p < 0.001) and 24.8 (21.6-28.9) vs.26.2 (24.5-30.8) %HRR, p < 0.01], respectively. Overweight children allocated more of their day to sedentary pursuits [385 (336-468) vs 297 (235-468) min/d, p < 0.001], and less time to moderate physical activity [381(321-457) vs. 460 (380-534) min/d, p < 0.01]. Nevertheless, because of the greater energy cost of a given task, total and active daily energy expenditure did not differ from those with a normal BMI.

Key points

  • The physical activity intensity for the entire day (PAI24) and for the waking part of day (PAIw) were lower in overweight than in normal weight individuals.
  • However, because the energy cost of activity is greater in those who are overweight, they do not differ in total energy expenditure or in active energy expenditure.
  • Normal children spend more time in moderate activity and less time in sedentary pursuits than overweight children.
Key words: Heart rate monitoring, activity patterns, energy expenditure, excess weight, obesity.  相似文献   
32.
We evaluated both the safety and efficacy of reteplase for treatment of acute arterial occlusion as well as outcomes based on treatment of the underlying lesion. From November 2000 to February 2004, reteplase was used to treat arterial occlusions in 81 patients. Catheter-directed intrathrombus thrombolysis was performed with reteplase (0.5 units/hr) continuous infusion. Percutaneous mechanical thrombectomy (Angiojet) was performed in 61% (n = 50) of patients prior to thrombolysis. Unmasking of significant lesions resulted in endovascular intervention (39.5%), open surgical repair (24.6%), or both endovascular and surgical repair (9.8%) of the lesion. No lesion was found in 25.9% of patients. Major and minor complication rates as well as restoration of patency, limb salvage, and amputation-free survival were evaluated. Eighty-one patients received reteplase therapy (median = 10.3 +/- 5.3 units, 19.5 +/- 7.4 hr) followed by next-day arteriogram to assess thrombus removal. Technical success was achieved in 96.2% (n = 78) of cases. Kaplan-Meier life table analysis revealed overall primary patency rates of 76.3%, 60.1%, and 51.6%, at 1, 6, and 12 months, respectively. Overall amputation-free survival rates were 86.4%, 76.4%, and 69.7% at 1, 6, and 12 months, respectively. When subdivided into postlysis intervention, the lysis-only group achieved increased patency (p = 0.0143) and increased limb salvage (p = 0.0219) at 1 year compared to the lysis and endovascular intervention and the lysis and surgical groups. The 30-day complication rate was 17.3% (n = 14), with a major complication rate of 4.9% (n = 4) and a minor complication rate of 12.3% (n = 10). There were no intracranial hemorrhagic complications. Intra-arterial catheter-directed infusion of reteplase for acute lower extremity ischemia is safe and efficacious, as shown by the low risk of bleeding complications, high limb salvage rates, and low mortality rates in this study. The complexity of the lesion that is unmasked through thrombolytic therapy is a predictor of patency and limb salvage.  相似文献   
33.
Objectives: This paper reports the prevalence and severity of caries in a group of 16‐month‐old American Indian children. Methods: The study is an ongoing longitudinal study of risk factors for caries in children from a Northern Plains Tribal community. Children were examined for caries and risk factor data collected at approximately 1, 4, 8, 12, and 16 months of age. Surface‐specific caries data were collected and the presence of precavitated “white spot” lesions was recorded at the subject level. Results: The mean age was 15.4 months for the sample of 232 children. Caries prevalence was 31.9 percent, while an additional 29.3 percent had white spot lesions only. Mean dmfs was 1.57, and ranged from 0 to 44 surfaces. Nearly 3 percent of all erupted tooth surfaces were affected and maxillary central incisors had the highest prevalence of caries (22 percent). Conclusions: Among the very youngest children, dental caries prevalence was very high among these American Indian children.  相似文献   
34.
AimsSelf-expanding metal stents provide rapid improvement of dysphagia in oesophageal cancer but are associated with complications. The aim of the present study was to test the effectiveness of an alternative treatment of combining biodegradable stents with radiotherapy.Materials and methodsA Simon two-stage single-arm prospective phase II trial design was used to determine the efficacy of biodegradable stents plus radiotherapy in patients with dysphagia caused by oesophagus cancer who were unsuitable for radical treatment. Fourteen patients were recruited and data from 12 were included in the final analyses.ResultsFive of 12 patients met the primary end point: one stent-related patient death; four further interventions for dysphagia within 16 weeks of stenting (41.7%, 95% confidence interval 15.2–72.3%). The median time to a 10-point deterioration of quality of life was 2.7 weeks. Nine patients died within 52 weeks of registration. The median time to death from any cause was 15.0 weeks (95% confidence interval 9.6–not reached).ConclusionThe high re-intervention observed, which met the pre-defined early stopping criteria, meant that the suggested alternative treatment was not sufficiently effective to be considered for a larger scale trial design. Further work is needed to define the place of biodegradable stents in the management of malignant oesophageal strictures.  相似文献   
35.
The expression of HLA-DR and HPCA-1 antigens (recognized by the L243 and BI.3C5 antibodies respectively) on adult human bone marrow cells was examined by fluorescence activated cell sorting and colony assays. Nearly all the (day 14) lineage restricted and multipotential colony forming cells analysed in methylcellulose cultures in the presence of added growth factors express HLA-DR and HPCA-1 determinants. Two colour cell sorting reveals that the lineage restricted HLA-DR positive progenitors express variable levels of BI.3C5 positivity whereas most of the multipotential progenitors, the multi-CFC or CFU-GEMM, are highly BI.3C5 positive. The isolated HLA-DR and BI.3C5 positive populations also contain haemopoietic precursors which adhere to and form colonies on pre-formed stromal layers. Thus, haemopoietic progenitors assayed in both types of culture system can be analysed and enriched by simultaneous two-colour sorting using anti-HLA-DR and BI.3C5 monoclonal antibodies. Similarities in the antigenic phenotype of such cells, however, precludes the use of these reagents for segregating growth factor-dependent from stroma-dependent progenitors.  相似文献   
36.
37.
38.
39.
We have investigated the effect of therapy forHelicobacter pylori gastritis on serum concentrations of pepsinogen I and II in 43 patients. In the 22 patients in whom therapy resulted in dramatic decrease in gastritis scores and in clearance of the bacteria, there was a highly significant (P=0.0001) fall in mean serum pepsinogen II from 13.3±0.8 to 7.9±0.7 μg/liter, and a less pronounced fall in pepsinogen I from 89.0±5.9 to 78.5±0.4 μg/liter (P=0.01). These changes resulted in a significant (P=0.01) increase in the pepsinogen I/II ratio. In contrast, nonsignificant declines of 3.5% and 11.6% were observed in mean pepsinogen I and II levels in the 21 patients whose gastritis failed to resolve histologically and whose infection did not clear. These findings suggest that serum pepsinogen levels, especially pepsinogen II, are a new tool that may be found to be clinically useful in evaluation of treatment outcome in patients withH. pylori-associated gastritis.  相似文献   
40.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号